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<html lang="en">
<head>
    <meta charset="UTF-8">
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    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title> 
    <script>        //因为是一进去就响应，弹出一个输入框，所以将script放入head中
        var a=prompt('请输入用户名');
        alert(a);
    </script>
</head>
<body>
   
</body>
</html>